A trailer (or connected cars) is used to haul luggage and goods at the Customs House, airports, or railway stations. The trailer can include a tractor as a motive power source and a plurality of flatcars or compartments hooked together in series hauled by the tractor. Radiation imaging inspection is often a requisite inspection means for the Customs House, airports and railway stations. The radiation imaging inspection refers to an inspection performed via an inspection passage including shielding rays, a radiation source, and an array detector which can receive the rays having permeated an inspected vehicle, where the inspected vehicle is hauled by a special traction means through the radiation beam for inspection. The inspection system usually comprises an accelerator system, a detector system, an image data acquisition system, a scanning device, and an operation & inspection system. In the prior technology, there are X-ray inspection devices for inspecting a passenger's luggage, and special inspection apparatuses for inspecting freight vehicles or container trucks. At present, there is not an inspection apparatus specially for inspecting a trailer.